It has been known that brown rice or wheat germ increases its gamma-aminobutyric acid content when being in contact with aqueous neutral or acidic solution in the range of appropriate temperature. For example, Patent Document 1 proposes a technique for producing sproutable food materials having an enriched content of gamma-aminobutyric acid by mixing rice brans or wheat embryos with buds with organic acid or inorganic acid to adjust their pH levels to 2.5 to 7.5, preferably 3.0 to 7.0, more preferably 5.5 to 6.0, in a region of weak to strong acidity, and soaking them in an aqueous solution adjusted at a temperature of 50° C. or lower (see Patent Document 1). In other words, the document describes a technique for enrichment of gamma-aminobutyric acid by soaking a specific sproutable food material in an aqueous neutral or acidic solution kept at an appropriate temperature to germinate the sproutable food material.
Cereals cause a germination reaction when being subjected to appropriate moisture and temperature conditions, thereby being softened to be easier to be eaten. However, the appropriate moisture and temperature conditions allow indigenous microorganisms (microorganisms) on the surface of cereals to grow all at once and emit bad smells. Thus, the germination process brings significant adverse effects that impair the original taste of sprouted cereals, and such adverse effects have not been successfully avoided up to now. One of measures for suppressing an unpleasant smell generated in the germination process is roasting after the germination. However, the roasting does not remove microorganisms. On the other hand, various kinds of germination procedures have been conducted to improve the taste of cereals while suppressing the generation of a smell by using some chemicals or the like to prevent the growth of microorganisms generated due to the germination.
A technique for improving the germination process has been proposed. Modifications of such a technique have been proposed such that, for example, chlorine water having sterilization and disinfection activities, a salt solution (saline) or an aqueous acidic solution having bacteriostatic and anti-microbial activities can be used to avoid an unpleasant smell or prevent a food taste from being deteriorated. In general, microorganisms prefer neutral or alkaline conditions rather than acidic conditions during proliferation. For example, one of traditional food preservation techniques is to place a pickled “ume” in a packed lunch or the like. The pickled “ume” contains “sodium chloride” with bacteriostatic activity and “citric acid” serving as an acidic material, and can suppress the growth of microorganisms and keep the quality of food for a certain period of time. However, the chlorine or salt water penetrates into the food material. As a result, there is a problem in that the food material may cause a specific smell or, in the case of salt water, the sproutable food material may have an increased salt concentration.
As an attempt to suppress the growth of microorganisms in the germination process by using salt water (an aqueous sodium chloride solution), Patent Document 2 proposes a technique for germination while suppressing the growth of microorganisms by using an aqueous solution containing at least sodium chloride, or by using deep-sea water (sea water). The solution of sodium chloride in pure water or the deep-sea water has a pH value in the range of, in general, a neutral region that extends from weak acidity to weak alkalinity (pH 6.0 to 8.0).
As an attempt to suppress the growth of microorganisms during the germination process by adjusting the pH of the aqueous sodium bicarbonate solution to acidic, Patent Document 3 describes a technique using an aqueous solution having a pH of 3.0 to 6.0 adjusted with organic acid or inorganic acid. In addition, Patent Document 4 describes a technique using an aqueous solution having an adjusted pH of 3.7 to 4.1. Another technique has been also reported for suppressing the growth of microorganisms; the technique directly restricts the amount of water to be supplied for germination to reduce the generation of a bad smell due to the growth of microorganisms attached on the surface layer of cereals. For example, Patent Document 5 describes a method for reducing the content of water to be added to cereals.
As described above, the growth of microorganisms and the generation of characteristic smells concomitant therewith can be successfully suppressed by the technique using an aqueous acidic solution, a salt solution (at neutral), or a limited amount of water. However, the successful suppression does not lead to an enrichment of glutamate in sprouted cereals to aggressively increase the content of delicious taste (so-called “umami”) ingredients in sproutable food materials. In addition, the successful suppression does not lead to an accelerated enrichment of gamma-aminobutyric acid in cereals, or does not lead to the expression of novel functionality based on the production of novel BDNFs for the brain and the body.
Glutamate, one of delicious taste (umami) ingredients, can be provided as a raw material of gamma-aminobutyric acid in the germination process of cereals. Patent Document 6 describes a technique using an aqueous solution containing glutamate in germination and a roasting treatment at high temperature after the germination to prevent cereals from having a decreased glutamate content and a deteriorated taste due to microorganisms.
As a germination technique involving addition of glutamate into an aqueous solution, for example, the Patent Document 7 proposes a method for enrichment of gamma-aminobutyric acid using an enzyme (glutamate decarboxylase reaction) contained in beans by mixing the glutamate-containing food material with the beans. Patent Document 8 proposes a technique for accelerating an enrichment of gamma-aminobutyric acid by addition of an extract from tea leaves, a glutamate-containing food material, into an aqueous solution for germination.
In other words, these techniques are provided for accelerating an enrichment of gamma-aminobutyric acid by addition of glutamate serving as a raw material of gamma-aminobutyric acid, a food material containing glutamate, or an extract of the food material in a germination process of a sproutable food material. However, as described in Examples below, the use of these techniques does not lead to an increase in glutamate content after germination more than one before the germination.
An aqueous sodium bicarbonate solution has been known to have anti-microbial properties. In addition, as described in Patent Documents 9 and 10, an aqueous sodium bicarbonate solution and an aqueous sodium sesquicarbonate solution have been known to work as herbicides that suppress the growth of plants.